A stack consists of a set of individual fuel cells being serially electrically coupled with each other through planar metal elements that separate them from each other in a sealed manner. These components, which are usually called separator plates or bipolar plates and consist of a rectangular planar metal sheet suitably shaped at the edges thereof, in combination with the electrodes and the matrix, have several functions:                they separate the anode area from the cathode area in a sealed manner, thereby preventing that the reacting gases may mix with each other;        they ensure a tight seal of the reacting gases towards the outside, by means of the shaping of the edges and the combination with the electrolyte matrix;        they contain therein the active components and the repetitive metal components making up the cell core;        in combination with the current collectors, they ensure that the reacting gases are properly distributed on the cell plane;        they ensure good conduction of the electrons produced by the reactions occurring within the cells.        
The stacks of molten carbonate fuel cells (MCFC) can be classified according to the type of treatment for the fuel gas and the typology of cell feed.
In the first case, the stacks can be characterized by an “internal reforming” or “external reforming”.
The “reforming” is the process through which an organic gas (such as CH4) is almost entirely turn into hydrogen (H2); in the case of “internal reforming”, this process takes place within the stack, and more precisely in the separator plates, whereas in the case of “external reforming” the organic gas entering the cell has already been transformed.
An example of stack with “internal reforming” can be found in U.S. Pat. No. 5,084,364.
Another distinctive element among the MCFC stacks is the type of feed of the fuel gas (generally H2 or CH4) and oxidant (generally air or O2) to the cell, which can be carried out by means of “internal or external manifolding”.
The separator plates for MCFC stacks with “external manifolding” are currently made from a planar metal sheet that is generally large as the cell active area, and by providing edges on the four sides of the sheet, which are folded in opposite directions. These edges take the shape of open flanges directed towards the inside of the sheet, with the same folding direction on the opposite sides thereof, but oriented in the opposite direction along the adjacent sides. Generally, these flanges are obtained from the same sheet making up the separator plate. An example of these separator plates can be found in U.S. Pat. No. 4,514,475.
Alternatively, the flange is made independently from the separator sheet, by simply using a smaller metal sheet being folded on itself such as to obtain a planar area required for attachment to the plate. An example of this type of flange can be found in U.S. Pat. No. 4,609,595.
In both cases, the flanges have to be suitably stiffened therein such as to resist the axial load to which they are subjected for the whole length thereof.
This stiffening is usually carried out by inserting suitable metal component within the flange, which are designed to ensure load resistance. This kind of components can be similar to strips of materials provided with a certain rigidity, which behave like springs.
The flanges have the double task of providing a tight seal for the gases towards the outside by using the sealing action of the matrix positioned thereon, as well as of defining the inner area of the separator plate in which the current collectors are positioned, thereby ensuring that the reacting gas properly passes therethrough.
Finally, due to the contact with the matrix along the outer areas, these flanges, whether they are directly obtained from the separator sheet or from a separated plane metal sheet, require a coating protecting them from the corrosion effects caused by the electrolyte.
The disadvantage of using flanges obtained from the same sheet making up the separator sheet is that a bulky component has to be manipulated while providing said protective coating, even when the areas covered by the flanges are minimal. This results in higher costs of the manufacturing process, greater hazard of possible manipulation injuries, and more difficult handling. Another disadvantage relates to the use of the same material both for the electrically active, planar part of the separator plate, and for the flanges. There results the need for selecting a conductive material and providing suitable protective coatings therefor, in order to give the same a good corrosion resistance in the flanges; this implies an increase in the manufacturing costs.
The prior art flanges provided independently from the separator plate suffer from the disadvantage of being anchored to the separator plate only by the friction between both contact surfaces; this causes relative movements occurring between the components during all the handling and assembly steps. Thereby, the precision required for stacking the cells is not ensured, which can therefore present themselves with different profiles and consequently with problems related with the planarity of the stack faces. Furthermore, strips of material are placed throughout the length of the prior art flanges in order to provide the required mechanical strength and rigidity. This operation is problematic during the assembly step, mainly with flanges having a closed profile and very long (>600 mm).